1. Field of the Invention
The invention concerns a high temperature component mounting system. In particular it relates to a mounting system for attaching together components made of materials having substantially different thermal expansion coefficients.
2. Description of the Prior Art
It is known in designing a mechanical joint between a first component of low-expansion material, for example a ceramic or ceramic composite, and a second material of higher-expansion material, such as a metal or metal alloy, to use a conical interface between the materials. Then, when thermal expansion or contraction occurs the thermally mismatched surfaces can slide one over the other to accommodate differential expansion.
A mounting arrangement of this type is known from my earlier published U.S. Pat. No. 5,022,805 entitled "Cantilever Mounting System for Structural Members having dissimilar Coefficients of Thermal Expansion". The arrangement described therein concerns the mounting of components of a gas turbine engine reheat system. In particular, a ceramic composite flameholder is attached to a metal bracket using a bolted-up, frusto-conical collar inside the hollow flameholder. The metal bracket, ceramic composite flameholder and metal collar are all formed with frusto-conical mating surfaces which converge to a common vertex on the axis of the flameholder. The cone angles are chosen to produce stress free metal/ceramic interfaces and relative differential movement takes place over the operating temperature range without inducing unnecessary stress or slackness. It is important that sufficient expansion clearance is provided within the joint to accommodate differential movement between the components without stressing the ceramic material. A drawback with this arrangement is the accuracy with which the frusto-conical surfaces must be formed, and the difficulty of forming the mounting surface in the interior of the flameholder. The ceramic composite production process lacks sufficient inherent accuracy to produce usable "as cast" interface surfaces so additional, expensive machining steps are required.
An improved arrangement for mounting ceramic composite reheat flameholders which avoids the above mentioned drawbacks, was described in my earlier published U.S. Pat. No 5,090,198. Each flameholder therein was formed with a dovetail at its proximal end which was engaged by angled faces formed on a retaining plate which, in turn, was bolted to a supporting structure. A clearance space remained between the dovetail end of the flameholder and the structure. When the retaining plate was bolted in place a resilient seal, or bias means, was sprung into this space in order to retain engagement between the non-metallic, low expansion flameholder and the metallic, high expansion support structure.
In practice it has been found difficult to achieve adequate preload in this type of arrangement and at high temperature the seal tends to creep. Consequently, over a period of time during use the force with which the flameholders are held in place tends to diminish.